In integrated optical circuits, thin monocrystalline layers are employed upon supporting substrates. Suitable substrates can either consist of a glass or of a crystalline material. The index of refraction of an applied thin crystalline layer adjacent the substrate must be higher than the index of refraction of the adjoining substrate so that light waves can diffuse in such thin layer by total reflection.
When such a thin crystalline layer is to be produced epitaxially, then the substrate must be a monocrystal with matched adjusted lattice constants, where electro-optical, magnet-optical, or acousto-optical effects in such thin layer and/or crystal are necessary for the achievement of modulators, switches, and the like.